Two neutral nonlinear complexes of HF and HArF with unusual bonding and vibrational characteristics were found to be stable relative to the constituent monomers by ab initio computations at various levels of theory. In the more stable complex, the proton of the HF molecule is bonded to the F atom of HArF, while in the less stable complex the F atom of HF is bonded to the proton of HArF. The intermolecular bonding in the less stable dimer is consistent with a hydrogen bonded complex, but calculations on the more strongly bound dimer suggest that the intermolecular bond in this case is predominantly ionic. (C) 2003 Published by Elsevier B.V.